This invention relates to a water-vapor-pervious warmth-retaining material. An objective is providing a novel material which possesses desirable perviousness to water vapor in addition to having the properties of a warmth-retaining, heat insulating material adapted to reflect light.
Heat insulating materials which are both water-vapor-permeable and waterproof are known such as, for example, the material described in U.S. Pat. No. 4,194,041.
Various metals and metallized materials possessing metallic gloss are capable of reflecting light and, as a result of dispersion of radiant heat, these materials manifest an advantageous warmth-retaining effect. This fact has been well known and has been utilized accordingly. There exist various substances which have metallic gloss. Among other substances of this class, aluminum possesses ease of fabrication and is comparatively low in cost. As a result of these advantages, aluminum is utilized extensively in the form of foil, particles, flakes, scales, and deposited layers. Aluminum foil, an aluminum layer vacuum-deposited on a substrate film of polyester or polyolefin, and a coating layer having powdered aluminum dispersed on alkyd resin or polyester resin all possess a substantial heat retaining effect but all fail to exhibit perviousness to water vapor. Thus, these material inevitably find limited use in application which require perviousness to moisture indispensably, for example, under conditions involving heavy perspiration or in the presence of steam. In the case of an insulating construction material using aluminum foil, for example, this inevitably collects dew because of changes in atmospheric temperature or temperature differnece inside and outside the insulated room. Consequently, it suffers from a shortened service life and impaired appearance. There are indications that efforts are being made to impart to foils and other materials which are impervious to water vapor the desired perviousness to moisture by punching holes therein. This measure requires that a number of holes be formed and a high ratio of hole area to unit surface area. Further, this measure impairs the valuable property of reflection of heat rays and reduces the warmth-retaining property as well. In the case of a coating layer which is formed by using a resin solution containing powdered aluminum, it has been proposed previously to confer perviousness to water vapor in the coating layer by incorporation of a hole-forming agent in the resin solution, subsequently expelling the hole-forming agent by extraction or vaporization from the coating layer after formation of the coating layer, and consequently providing the coating layer having a porous texture attended by perviousness to water vapor. Despite these efforts, the coating layer so formed generally fails to acquire the needed perviousness to water vapor. The work involved in such a construction is complicated. Moreover, the introduction of such fine pores can adversely affect the properties of the resin and seriously degrade the strength and elongation of the coating material.